Most anglers and biologists feared that it was inevitable that whirling disease would find its way into Strawberry Reservoir, one of Utah's most important flat-water trout fisheries.

That inevitability occurred this week when fish pathologists from the Division of Wildlife Resources tested 60 kokanee salmon collected at Strawberry and found spores from the parasite in two of them.

The good news for anglers is that, while whirling disease is still a major concern, much has been learned about how to counteract its effects on a fishery. The disease was first discovered in Utah in 1991 in a private fish hatchery in Wayne County owned by the family of then-Utah Gov. Mike Leavitt.

Whirling disease doesn't harm people. But the disease can be fatal to small trout and salmon. Fish that contract the disease often swim in a whirling motion before they die, thus giving the disease its name.

"This would have been a much different matter if it had happened in the mid-1990s," said Roger Wilson, chief of the DWR's aquatic section. "We know a lot more about whirling disease and what happens post infection. It's still a great concern, and we would prefer not have it. We are in a situation where we can live with this parasite, even in a place like Strawberry."

Wilson said biologists expected to find whirling disease at Strawberry sooner. It can be moved by anglers, boats, flowing water or birds. The disease was found several years ago in the West Fork of the Duchesne River. Water from the river eventually empties into Strawberry Reservoir through an aqueduct and collector system.

Veteran Utah angler and Fish Tech tackle shop owner Byron Gunderson was not surprised by the discovery.

"It was inevitable," he said. "It was just a matter of time. That stuff leaks from here to there, so it wasn't particularly unexpected."

Wilson said that the disease affects mostly small trout. Once trout grow from fry to fingerling size, the chances of the fish developing clinical signs of the disease diminish rapidly.

Biologists plant rainbow and cutthroat into Strawberry that are a minimum of eight inches long, a size not affected by the disease. And most of the rainbows planted into the big reservoir are a whirling-disease-resistant strain known as Harrison-Hoffer. Wilson said that the agency would expand the use of the strain at Strawberry in the future.

An audit issued to the Utah Legislature on the DWR's hatchery program this week was somewhat critical of the agency for its hatchery program. But Wilson said the way Strawberry is managed shows why the state's hatchery system sometimes needs to produce bigger fish that cost more money.

All of the rainbow trout in the reservoir are stocked by the DWR, which also stocks kokanee and cutthroat. In addition, the Bear Lake cutthroat trout planted in Strawberry are also more resistant than some other cutthroat strains.

"All of these things we come up with on the management end make it more difficult on the hatchery system," he said.

Another major concern is how the disease might affect cutthroat and kokanee trout that spawn naturally in Strawberry's tributaries. Those fish also add to the number of fish in the reservoir. Kokanee salmon are particularly susceptible to whirling disease.

Wilson said that 15 to 20 percent of the adult age cutthroat produced at Strawbery come from its tributaries, though that percentage has been as high as 65 percent in the past. An aggressive stream restoration program on the Strawberry River could mean less habitat for the parasite host that causes whirling disease. Most of the cutthroat caught by anglers, though, are hatchery raised.

"I don't know how successful the spawn has been as far as the cutthroats go," said Gunderson. "Few of my customers ever catch cutthroats. Rainbow planting has been successful because they have been raising fish to a larger size before they grow up."

He said most Strawberry bait anglers catch rainbows, and fly and lure enthusiasts practice catch-and-release angling on the reservoir east of Heber City.

"I don't think it will have that big of an effect on Strawberry," said Gunderson.

DWR biologists hope that is the case.

"Rest assured that we'll continue to take the appropriate steps to ensure the continued quality of Utah's most important cold water fishery," said Wilson.

wharton@sltrib.com

Twitter: @tribtomwharton